The present invention relates to improved semiconductor laser devices and has particular reference to semiconductor laser devices in which one or more of the active layers is made sufficiently thin that size quantization occurs.
Semiconductor lasers based on conventional heterostructures, for example of GaAs-AlGaAs or GaInPAs-InP, are commercially available and represent one of the important components used in the fields of optical communications technology, optical data storage and integrated electrooptical circuitry (integrated optics). A useful summary of the charateristics of such devices is provided in the paper "Heterostructure Semiconductor Lasers Prepared by Molecular Beam Epitaxy" by W. T. Tsang published in the IEEE Journal of Quantum Electronics, vol. QE-20, No. 10, October 1984, pages 1119 to 1132. This articles also discloses a variety of novel semiconductor laser structures which include at least one ultra-thin layer disposed in the active zone of the device, with this ultra-thin layer being sufficiently thin that size quantization occurs which has far reaching effects on the physical properties of the laser devices. Each of the known types of semiconductor laser devices lases at a wavelength particular to that device and it is only possible to shift this wavelength by a small amount generally not greater than 5 nm. This is however a significant restriction because it would be desirable in many potential applications of semiconductor laser devices to have available a device which is capable of operating at two or more distinct emission wavelengths, for example for "wavelength multiplexing". A satisfactory semiconductor laser device of this kind has however, so far as can be ascertained, not yet been reported.